sdp.js: Support msid lines with ssrc for backwards compatibility
sdp.js: Support msid lines with ssrc for backwards compatibility

Can be removed eventually

adozenlines/openwebrtc,multipath-rtp/openwebrtc,stefhak/openwebrtc,shoreflyer/openwebrtc,stefhak/openwebrtc,alessandrod/openwebrtc,shoreflyer/openwebrtc,multipath-rtp/openwebrtc,EricssonResearch/openwebrtc,adozenlines/openwebrtc,alessandrod/openwebrtc,philn/openwebrtc,stefhak/openwebrtc,EricssonResearch/openwebrtc,danielwegener/openwebrtc,shoreflyer/openwebrtc,EricssonResearch/openwebrtc,pererikb/openwebrtc,danielwegener/openwebrtc,stefhak/openwebrtc,philn/openwebrtc,philn/openwebrtc,EricssonResearch/openwebrtc,shoreflyer/openwebrtc,alessandrod/openwebrtc,EricssonResearch/openwebrtc,alessandrod/openwebrtc,shoreflyer/openwebrtc,multipath-rtp/openwebrtc,multipath-rtp/openwebrtc,philn/openwebrtc,multipath-rtp/openwebrtc,EricssonResearch/openwebrtc,adozenlines/openwebrtc,pererikb/openwebrtc,adozenlines/openwebrtc,pererikb/openwebrtc,danielwegener/openwebrtc,danielwegener/openwebrtc,pererikb/openwebrtc,philn/openwebrtc,stefhak/openwebrtc,alessandrod/openwebrtc,stefhak/openwebrtc,multipath-rtp/openwebrtc,alessandrod/openwebrtc,danielwegener/openwebrtc,philn/openwebrtc,pererikb/openwebrtc,pererikb/openwebrtc,shoreflyer/openwebrtc,pererikb/openwebrtc,philn/openwebrtc,multipath-rtp/openwebrtc,shoreflyer/openwebrtc,adozenlines/openwebrtc,adozenlines/openwebrtc,danielwegener/openwebrtc,EricssonResearch/openwebrtc